The present invention relates to an image writing control unit and particularly to a control unit for writing image data to a memory area referred to as a frame buffer with each bit corresponding to each pixel of image.
Conventionally, in such an image writing control unit, when 1 word of image data is written into the frame buffer with positioning said word of the image data over a word boundary of memory forming the frame buffer, 1 word of the image data are shifted by necessary bit number (X bits) as shown in FIG. 1, and thereafter by time division 1 word of high order side after shifting is accessed to address N in the frame buffer and then 1 word of low order side after shifting is accessed to address N+1 in the frame buffer. Therefore access time of 2 words of image data into the frame buffer is required for said word of image data bestriding a word boundary.